arch-arm: Add an Armv8.1 ArmRelease object

Change-Id: I5638deb77a165bec1ee47d8f1b2bac31647f173a
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/51016
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

src/arch/arm/ArmSystem.py

@@ -104,6 +104,12 @@ class ArmDefaultRelease(Armv8):
         'FEAT_HPDS', 'FEAT_VMID16', 'FEAT_RDM', 'FEAT_SEL2'
     ]
 
+class Armv81(Armv8):
+    extensions = Armv8.extensions + [
+        'FEAT_LSE', 'FEAT_VHE', 'FEAT_PAN',
+        'FEAT_HPDS', 'FEAT_VMID16', 'FEAT_RDM'
+    ]
+
 class ArmSystem(System):
     type = 'ArmSystem'
     cxx_header = "arch/arm/system.hh"